1. Field of the Invention
The present invention relates to end covers for motor rotors, and, more particularly, to a magnetically driven motor rotor having end covers for retaining magnetic bodies.
2. Description of Related Art
A typical motor is comprised of a stator and one or more rotors, wherein the stator is a static component used to provide the magnetic field and the rotor is rotatable according to the magnetic field. The rotor is constituted by a turning spindle and one or more permanent magnets, wherein the turning spindle is typically composed of a stack of silicon steel plates connected and stacked on one another, wherein each permanent magnet is adhered to the peripheral wall of the rotor and faces the stator. However, the permanent magnets are liable to come off due to external usage factors since the magnets are only adhered to the stator, and the detachment of a magnet can cause the rotor to not be able to function normally and possibly even get stuck in the stator.
The external usage factors, as mentioned above, refer to a variety of conditional factors and often involve temperature and humidity factors in the environment where a motor is used. Due to the difference in the thermal expansion coefficient between different constituent components of the permanent magnet and the spindle typically made of silicon steel plates, detachment of the rotor easily occurs when the motor is used under extreme conditions, for example, in a frigid zone or in a very humid zone such as when the motor is used under water. Under such conditions, the metal plates (i.e. silicon steel plates of the turning spindle) can gradually become rusty and the accumulated rust can push against the solidified adhesive layer such that the permanent magnets may detach and come off as a consequence. While such external usage factors do not directly or immediately cause a motor to be defective, the lifespan of the motor is adversely affected by such usage factors. Therefore, improving and overcoming such external environmental factors is as important as the motor per se and cannot be ignored in attempting to design a motor with prolonged lifespan.
To improve the above issues associated with the adhesion of magnets to a motor, several improved techniques have been disclosed in Taiwanese Invention Patent Publication No. 595072, Taiwanese Utility Publication No. 579131, Taiwanese Utility Publication No. 412100, Taiwanese Utility Publication No. M302825 and Taiwanese Utility Publication No. M312835.
It is a common practice to use gap intervals to assemble the spindle with permanent magnets around the peripheral wall of the spindle, such that each of the permanent magnets can be accommodated into a respective trench formed therein. However, problems during assembly often occur due to differing manufacturing and processing techniques used for the silicon steel plates and the permanent magnets, which often increases the defect ratio during assembly since the permanent magnets are fragile and tend to break easily during the assembly process in which they are embedded in respective trenches.
As shown in FIG. 1, Taiwanese Utility Publication No. 412100 discloses a motor rotor structure 1 composed of a stack of silicon steel plates 11, permanent magnets 13, fastening pins 15 and two end covers 17. The plurality of silicon steel plates 11 are stacked on one another and connected to constitute a turning spindle, wherein a plurality of fixing trenches are disposed along the peripheral wall of each silicon steel plate 11 to engage with the fixing pins 15, thereby embedding permanent magnets 13 disposed around the peripheral wall of the spindle formed by a stack of silicon steel plates 11; that is, each permanent magnet 13 is retained between two adjacent fixing pins. An end cover 17 is disposed at each of the two ends of the spindle in order to clamp and hold the permanent magnets 13 and fixing pins 15 in place such that they don't fall out from either end of the spindle.
However, the foregoing method requires the use of additional components—the fixing pins 15—in order to retain the permanent magnets 13, as well as two end covers 17 to prevent compatibility differences from existing therebetween as a result of processing precision, thereby increasing not only costs due to the extra components, but also the costs for assembly and material storage, and further resulting in an increase of the defect ratio during assembly due to assembly compatibility problem. There is a large precision difference in fabricating fixing trenches on each of the stack of silicon steel plates and processing the permanent magnets 13, thus leading to difficulty in controlling precision during assembly due to precision incompatibility (such as a loose match or an excessively tight match due to differences in processing). For example, due to their fragile nature, the permanent magnets 13 can easily be crushed or broken during insertion of the fixing pins 15 in an excessively tight match, causing an increase of defect ratio and thus higher manufacturing costs.
With reference to FIG. 2, Taiwanese Utility Publication No. 595072 discloses a motor rotor structure 2 composed of a spindle 21, a plurality of permanent magnets 23 and holding teeth 25. The spindle 21 is integrally formed of silicon steel material instead of combining a stack of silicon steel plates as commonly used in the prior art. A plurality of interspaced coupling protrusions 211 are formed around the outer peripheral wall of the spindle 21. Each of the permanent magnets 23 is retained between two adjacent coupling protrusions 211 disposed around the outer peripheral wall of the spindle 21, and each holding tooth 25 is inserted into a respective trench formed corresponding in position to a coupling protrusion 211, such that each permanent magnet 23 is secured in position by two adjacent holding teeth 25.
However, the holding teeth 25 need to be made such that they correspond to the size and shape of the permanent magnets 23, and also the coupling trenches need to match up with the coupling protrusions 211, thus increasing difficulty in fabrication and matching precision as well as the costs for fabricating, assembling and storing the holding teeth 25. Further, the holding teeth 25 need to be tightly engaged with the permanent magnet 23 to ensure secure fastening; however, vibrations and loosening of the permanent magnets 23 may occur due to imprecision resulting from processing differences, especially when being subjected to environmental usage factors.
Taiwanese Utility Publication No. 579131 discloses a motor rotor structure of an embedding type characterized by disposing embedding grooves in existing magnetic gap trenches of magnetic conductive plates of the spindle; disposing coupling flanges along the peripheral wall of the opening of the embedding grooves; and disposing assistive positioning plates having a shape corresponding to a magnetic-conductive pieces to engage with one another, wherein the length of the assistive positioning plates only couple to an end of each permanent magnet and no assistive positioning plates are disposed between the gap trenches and the magnets.
However, it is necessary to taper and sharpen the end of each permanent magnet in order for it to be embedded in the groove, such that the end of the magnet suffers from greater stress and is liable to break under pressure, thus compromising the effect of fastening. Further, it is difficult to use a grinding wheel to sharpen a typical permanent magnet that has a thickness of approximately only 3.5 mm in order to obtain satisfactory assembly compatibility with the embedding groove to ensure secure fastening, thus compromising the yield rate in assembling such a motor rotor.
Taiwanese Utility Patent No. M312835 discloses a mechanism for fastening the permanent magnets to a motor rotor structure, characterized by clamping the permanent magnet in between two hollow compressed rings, wherein a plurality of protruding pillars are disposed on one of the hollow compressed rings with each spaced apart at an equal gap interval therebetween, and wherein each protruding pillar comprises a coupling portion disposed on both sides thereof and a fastening aperture disposed in between two coupling portions, while the other hollow compressed ring is formed with a fixing aperture to be axially penetrated therethrough. Each of the permanent magnets comprises a connecting portion on both sides thereof that is adapted to correspondingly engage with a respective coupling portion such that the permanent magnet can be embedded in between two adjacently disposed pillars; and further a plurality of fastening elements, such as bolts, are used to lock each of the fixing apertures to securely assemble the hollow compressed rings, thereby clamping each of the permanent magnets in between the two hollow compressed rings.
However, there are still several drawbacks in employing the above technique: first, the use of locking bolts is problematic because bolts are liable to conduct magnetism and affect the magnetic field; second, the use of tools for locking bolts makes the assembly process cumbersome and inconvenient; third, the use of a total of eight bolts requires the same amount of nuts with the same weight in order to maintain rotational stability under gravity and that further increases the time and costs and complicates processes in manufacture; and fourth, easy loosening and dislocating of the bolts can occur with vibration due to the rotating motions of the motor rotor, resulting in dislocation and detachment of the permanent magnets and thus compromising the lifespan of the motor and the motor rotor.
Summarizing the above, it is desirable and highly beneficial to develop a novel motor rotor structure that can provide a secure fastening effect with a simplified structure for easy assembly that decreases the number of components required and avoids external environmental factors affecting the usage lifespan, and also prevents the magnets from breaking and thus increasing the yield rate during assembly.